Its lateral border is thick and irregular, and presents three or four tubercles for the tendinous origins of the deltoid. Its inferior surface is smooth and concave. Its superior surface, directed upward, backward, and lateralward, is convex, rough, and gives attachment to some fibers of the deltoideus, and in the rest of its extent is subcutaneous.

It starts from the base of acromion which marks its projecting point emerging from the spine of scapula. The acromion forms the summit of the shoulder, and is a large, somewhat triangular or oblong process, flattened from behind forward, projecting at first lateralward, and then curving forward and upward, so as to overhang the glenoid fossa. It articulates with the clavicle (collar bone) to form the acromioclavicular joint. The acromion is a continuation of the scapular spine, and hooks over anteriorly. Together with the coracoid process it extends laterally over the shoulder joint. In human anatomy, the acromion (from Greek: akros, 'highest', ōmos, 'shoulder', PL: acromia) is a bony process on the scapula (shoulder blade).

Is clavicle a flat bone